Power supplies are used to supply power to power-consuming loads. "Load shedding" is a term which refers to reducing the power demands on a power supply upon the occurrence of a predetermined condition. Preferably, such load shedding should be accomplished in a manner which maintains, if at all possible, some minimum acceptable level of load operation.
In electric utility companies, load conditions are commonly sensed and, upon the occurrence of some maximum demand level, the power generating equipment of the utility company reduces its output voltage level to avoid damage to such equipment and power distribution network extending therefrom. This technique has long provided satisfactory results but is not applicable to certain power supply applications. For example, in certain systems, the automatic reduction of the power output by the supply may render the supplied loads inoperative or can suddenly reduce their performance to an unacceptable level. One example of such an application is in a communications system wherein such reduction can cause a complete or significant loss of communications capabilities.
Communications equipment is often designed with one or more power supplies which feed a number of power-consuming communications loads. The capacity of such supplies is generally determined upon initial system design to supply sufficient power for the intended loads. However, with time, the communications capabilities of such systems are typically expanded which, in turn, are often accompanied by a substantial increase in the demand placed upon the power supply. Indeed, the increased demand may, at times, exceed the maximum capabilities of the initially-sized power supply. To avoid this result, the initially installed power supply can be designed with a power capability far in excess of that initially required. This approach, while acceptable from a performance standpoint, results in an increased communications system cost which may exceed system objectives. Another approach is to retrofit a larger capacity power supply into a communications system when increased communications capabilities are added and the power demand approaches or exceeds that of the installed power supply. The problem with this approach is that the retrofit of a larger capacity power supply may not be possible due to size constraints, or the resulting heat transfer requirements of the larger supply cannot be provided by the existing equipment housing, or the retrofit is expensive and requires rendering the communications system inoperable for an undesirable length of time.